Rules & Regulations of the State of Tennessee
Title 0400 - Environment and Conservation
Subtitle 0400-45 - Water Resources (Water Supply)
Chapter 0400-45-07 - Rules and Regulations Applied to the Safe Dams Act of 1973 (Transferred from 1200-05-07)
Section 0400-45-07-.07 - DESIGN STANDARDS FOR NEW DAMS
Universal Citation: TN Comp Rules and Regs 0400-45-07-.07
Current through March 23, 2025
(1) Design of Dams. Designs of dams shall conform to accepted practices and procedures of the engineering profession. Design references developed by the U.S. Army Corps of Engineers, Soil Conservation Service, and the Bureau of Reclamation may be used although the limiting criteria must be in accordance with these rules.
(a) All dams will be considered on an
individual basis and reviewed in accordance with prevailing practices that are
currently accepted by the engineering profession.
(b) All structures other than Category 3 dams
constructed before 2008 shall be designed to withstand seismic accelerations of
the following intensities: Zone 1=0.025g, Zone 2=0.05g, Zone 3=0.15g. Zones
refer to "Geologic Hazards Map of Tennessee" by Robert A. Miller, 1978. All
dams constructed during or after 2008 shall be designed to withstand the peak
ground acceleration for an earthquake with a 10% probability of exceedance in
50 years as determined by the United States Geological Survey at the time the
construction permit is issued. A different peak ground acceleration may be used
if site specific studies using accepted engineering practices determine that a
different value is appropriate.
(c)
A complete engineering report, plans, and specifications shall be submitted for
each dam.
(d) A complete
geotechnical report shall be submitted as an integral part of the engineering
report for all Hazard Potential Category (HPC) 1 and 2 dams (defined in Rule
0400-45-07-.05). For HPC 3 dams, sufficient investigation will have to be made
to determine if the site and the fill material to be used are suitable, and
this information will have to be included in the engineering report.
(e) A hydrologic/hydraulic analysis shall be
submitted as an integral part of the engineering report for all dams. A breach
analysis shall be submitted for all HPC 1 and HPC 2 dams and, for the former,
shall be included in the Emergency Action Plan. The breach analysis must use
surveyed cross sections at all stations where homes or other structures may be
flooded. A sunny-day breach shall be modeled with the impoundment at the
elevation of the emergency spillway invert when the failure begins, or, if
there is no emergency spillway, at the elevation of the inlet of the principal
spillway. Breach modeling under sunny-day, overtopping, or any other
conditions, is site specific.
(f)
All Category 1 dams shall submit to the Commissioner an Emergency Action Plan.
This plan shall include, but not be limited to, the following:
1. Inundation information and an inundation
map based on the breach analysis.
2. Procedures for notification of people
downstream and law enforcement and other government agencies.
3. Resources for emergency actions such as
contractors, equipment supply businesses, etc.
(g) Design calculations for all major
components of the structure, i.e., spillways, pipes, etc., shall be included in
the engineering report.
(2) Principal Spillways.
(a) All component parts of the principal
spillway except attached gates and trash racks will be of equal durability. The
structural design criteria and detailing of such spillways will conform to
recognized standards and codes of practice.
(b) In requiring the capacity of the
principal spillway, the Commissioner may consider:
(1) the benefits that accrue to the reduction
of the discharge rate,
(2) damages
that may result from prolonged storage in the reservoir,
(3) damages that may result from prolonged
outflow,
(4) the possibility of
occurrence of significant runoff from two or more consecutive storm events
within the time required to empty the reservoir, and
(5) limitations in water rights or other
legal requirements.
1. All conduits under a
dam shall support the external loads imposed with an adequate factor of safety.
They must withstand the internal hydraulic pressures without leakage under full
external load and settlement. They must convey water at the design velocity
without damage to the interior surface of the conduit.
2. Principal spillway conduits under earth
dams shall be designed to support fill heights greater than the original
constructed height where there is a reasonable possibility that it may become
desirable to raise the embankment height at a later date to incorporate
additional storage.
3. Principal
spillway conduits shall be of reinforced concrete pipe, cast-in-place
reinforced concrete, ductile iron pipe, or plastic pipe. Fill height and
foundation conditions require special considerations for ductile iron pipe and
plastic pipe so that each use will be checked on an individual basis; cradling
or encasement in concrete may be required. Welded steel pipe is not acceptable
for Category 1 and Category 2 dams, and corrugated metal pipe is not acceptable
for any class of dam.
4. Principal
spillway conduits shall be field tested for watertightness before backfilling.
This requirement as well as the method of testing shall appear on the plans or
in the specifications.
5. Rigid
principal spillway conduits shall be designed as positive projecting
conduits.
6. All reinforced
concrete water pipe - steel cylinder type - prestressed, all reinforced
concrete water pipe - steel cylinder type - not prestressed, and all reinforced
concrete water pipe - noncylinder type - not prestressed, shall meet the AWWA
specifications effective at the time of application.
7. Elliptical or other systems of
reinforcement requiring special orientation of pipe sections are not permitted
in pipe drop inlet barrels.
8.
Reinforced concrete pipe, with or without cradles, shall be designed to support
at least 12 feet of earth fill above the pipe at all points along the
conduit.
(c)
The minimum inside diameters of pipes shall be as follows:
1. Category 3 dams: The minimum diameter of
the principal spillway barrel will be 18 inches for fill heights up to 50 feet
and 24 inches for greater heights; or
Where the drop inlet is designed hydraulically in such a way that the flow in the barrel under all possible conditions of discharge and foundation consolidation is positively known to be open channel flow with the water surface in the conduit subject to atmospheric pressure only, the minimum diameter shall be 18 inches; or
Where welded steel pipe is used, the principal spillway shall be designed in accordance with conditions presented in subparagraph (e) of this paragraph.
2. Category 2
dams: The minimum diameter of the principal spillway barrel shall be 24
inches.
3. Category 1 dams: The
minimum diameter of the principal spillway barrel shall be 30 inches.
4. Smaller conduits may be used if detailed
calculations show them to be hydraulically and structurally adequate and all
other requirements of this rule 1200-5-7-.07 are met.
(d) Where the barrel and cradle or bedding
are to rest directly on firm bedrock thick enough so that there is essentially
no foundation consolidation under the barrel, the cradle under the pipe need
not be articulated.
(e) Principal
spillways of welded steel pipe may be used for Category 3 dams under the
following conditions, all of which must be met:
1. The minimum diameter of the barrel will be
18 inches.
2. The height of fill
over the pipe will be less than 35 feet.
3. Welded steel pipe conduits are to conform
to American Society of Testing Materials (ASTM) specifications A53, A120, A135,
A139, or A134 and are to be structurally designed as rigid pipe. A joint
extension safety margin of 1.5 inches is to be provided for conduits on
yielding foundations. Welded pipe is to be protected by an approved exterior
coating.
(f) Conduit
joints will be designed and constructed to remain water tight under maximum
anticipated hydrostatic head and maximum probable conditions of joint opening,
including the effects of joint rotation, and must have a margin of safety where
required.
(g) Trash racks will be
designed and built to provide positive protection against clogging of the
spillway at any point. The average velocity of flow through a clean trash rack
will not exceed 2.5 feet per second with the water elevation in the reservoir
five feet above the top of the trash rack or at the crest of the emergency
spillway, whichever is lower. Velocity will be computed on the basis of the net
area of opening through the rack.
For dry dams, a trash rack may be used in lieu of a ported concrete riser. The principal spillway trash rack will extend sufficiently above the anticipated sediment elevation at the inlet to provide full design flow through the spillway with velocities through the net area of the trash rack above the sediment elevation not in excess of two feet per second when the water surface in the reservoir is five feet above the top of the trash rack.
(h) All
closed conduit principal spillways designed for pressure flow will have an
anti-vortex device.
(3) Drawdown Facilities.
(a) All new dams shall
have a drawdown facility. This facility shall be capable of draining the
reservoir in ten (10) days or less. It may be assumed that this requirement has
been met if seventy-five (75) percent of the liquid volume from the normal
water storage elevation has been evacuated in the ten (10) day period. The use
of a longer period must be justified.
(b) The necessary drawdown facility for any
dam shall be made an integral part of the principal spillway structure if the
principal spillway configuration warrants it, but in no case will the drawdown
facility be valved on the downstream side of the embankment. Siphon facilities
will be accepted after proper engineering justification.
(c) Subparagraph (b) of this paragraph does
not apply in the case of a water supply line through the dam, but in such cases
provision must be made for a positive shutoff on the upstream side of the
structure.
(d) Drawdown systems
shall be maintained in an operable condition. Drawdown valves shall be opened
and closed at least annually to ensure operability.
(4) Emergency Spillways.
(a) An emergency spillway shall be provided
for each structure, unless the principal spillway is large enough to pass the
routed freeboard hydrograph discharge and the debris that comes to it. A
conduit type principal spillway having a barrel with a cross-sectional area of
20 square feet or more, an inlet which will not clog, and an elbow designed to
facilitate the passage of debris, is the minimum size and design that may be
utilized without an emergency spillway. If a principal spillway of this type
and size is not provided, danger from clogging requires the use of an emergency
spillway regardless of the volume of storage provided.
(b) A single uncontrolled open channel
spillway may be used for all purposes provided it is designed to accommodate
all discharges, including the freeboard storm, without damage to the structure.
However, a positive means to drain the reservoir must also be
provided.
(c) Emergency spillways
shall be proportioned so that they will pass the freeboard hydrograph at the
safe velocity determined for the site. They shall have sufficient capacity to
pass the freeboard hydrograph with the water surface in the reservoir at or
below the maximum storage elevation.
(d) Minimum Freeboard Design Storms
| Size | Freeboard Design Storm (6 Hour) |
| Small | 1/2 PMP |
| Intermediate | PMP |
| Large | PMP |
(e) All dams shall have an emergency spillway
system with capacity to pass a flow resulting from a 6 hour design storm
indicated in subparagraph (d) of this paragraph for the size corresponding to
the dam. Any new dam constructed between October 3, 1987, and February 19,
2001, shall be required to pass the Freeboard Design Storm specified in
subparagraph (3)(b) of Rule 0400-45-07-.06. However, if the applicant's
engineer provides calculations, designs, and plans to show that the design flow
can be stored, passed through, or passed over the dam without failure
occurring, or if he can successfully demonstrate to the Commissioner that the
dam is a safe structure and can certify that the dam is sufficient to protect
against probable loss of human life downstream, said dam design may be approved
by the Commissioner. The establishment of the criteria in subparagraph (d) of
this paragraph does not eliminate the need for sound engineering judgment but
only establishes the lowest limit of design considered acceptable.
(f) The relationship between the water
surface elevation in the reservoir and the discharge through the emergency
spillway shall be evaluated by computing the head losses in the inlet channel
upstream of the control section, or if a control section is not used, by
computing the water surface profile through the full length of the spillway.
Manning's formula will be used to evaluate friction losses and determine
velocities.
(g) The freeboard
hydrograph shall be routed through the reservoir starting with the water
surface at the elevation of the principal spillway inlet.
(h) A vegetated earth or unlined emergency
spillway shall be approved when computations indicate that it will pass the
design storm without jeopardizing the safety of the structure. The risk of
recurring storms, excessive erosion, and inadequate vegetative cover will be
considered acceptable in such a spillway when its average frequency of use is
predicted to be not more frequent than once in 25 years for Category 3 dams,
once in 50 years for Category 2 dams, and once in 100 years for Category 1
dams.
1. Vegetated and earth emergency
spillways may be open channels and may consist of an inlet channel, a control
section and an exit channel. Subcritical flow exists in the inlet channel and
the flow may be supercritical in the exit channel.
2. Vegetated emergency spillways may be
trapezoidal in cross-section and shall be protected from damaging erosion by a
grass cover. They shall be used at sites where a vigorous grass growth can be
sustained by normal maintenance without irrigation.
3. Earth spillways may be used in those areas
where vegetative growth cannot be maintained. They are similar to vegetated
spillways but are designed for lower permissible velocities and less frequent
use. The needed maintenance after a flow occurs is the responsibility of the
certificate holder.
4. Earth and
vegetated emergency spillways are designed on the basis that some erosion or
scour is permissible if its occurrence is infrequent, if maintenance facilities
are provided, and if damage from a severe storm, as represented by the
freeboard inflow hydrograph, will not endanger the structure.
5. A Manning's ''n'' of 0.040 may be used for
determining the velocity and capacity in vegetated spillways. Permissible
velocities in earth spillways may be based on an "n" value of 0.020 but the
capacity of earth spillways will be based on an appraisal of the roughness
condition at the site.
6. When the
anticipated average use of a vegetated emergency spillway is more frequent than
once in 50 years, the maximum permissible velocity will be in accordance with
the values given below. The values may be increased 10 percent when the
anticipated average use is not more frequent than once in 50 years or 25
percent when the anticipated average use is not more than once in 100 years.
The maximum velocity limitations given below for vegetated or earth emergency
spillways apply to the exit channel.
7. The values given will be the upper limit
for all grasses. Values for grasses or grass mixtures will be determined by
comparison with the values shown, with due consideration given to the growth
characteristics and density attained in the local area by the species under
consideration.
8. Where bona fide
studies or investigations have been made to determine the permissible velocity
for a specific soil and site, these values may be used in lieu of those shown
below.
9. Maximum Permissible
Velocities for Vegetated Earth Spillways.
Grasses or Grass Mixtures
| Soil Type | Slope | Maximum Permissible Velocity |
| Erosion Resistant | 0-5 % 5-10% | 8.0 fps 7.0 fps |
| Easily Erodible | 0-5 % 5-10% | 6.0 fps 5.0 fps |
(5) Earth Embankments.
(a) Sufficient freeboard shall be provided to
prevent overtopping with the passage of the freeboard hydrograph plus the
additional freeboard required by the site for wave action.
(b) The top width of earth embankments will
not be less than the value given by the following equation:
where H=height of embankment in feet.
W=minimum top width of embankment in feet.
(c) The earth embankment will be riprapped or
have other wave erosion protection provided over the full range in stage
between three feet above and below the normal pool elevation.
(d) All dams shall be designed and
constructed to prevent the development of instability due to excessive seepage
forces, uplift forces, or loss of materials in the embankment, abutments,
spillway areas, or foundation. Seepage analysis for design and inspection
during construction shall be in sufficient detail to prevent the occurrence of
critical seepage gradients. All dams permanently impounding water shall be
constructed with an embankment toe drain with drain pipes installed to
discharge the seepage.
(e) All dams
shall have a permanent bench mark monument located near the embankment in
undisturbed soil or in bedrock. This bench mark shall be detailed in the plans
and specifications.
(f) All dams
shall be protected from surface erosion by appropriate vegetation or some other
type of protective surface such as rip-rap or paving and shall be maintained.
Examples of appropriate vegetation include, but are not limited to, Bermuda
grass and fescue. All inappropriate vegetation such as honeysuckle, briers,
bushes and trees shall be kept off the dam by routine mowing.
Authority: T.C.A. §§ 69-11-101 et seq., and 4-5-201 et seq.
Disclaimer: These regulations may not be the most recent version. Tennessee may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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